Spectroscopic and Computational Elucidation of Binuclear Non-Heme Iron Enzyme Intermediates
소속 :
연사 : Prof. Park Ki Young(KAIST)
일시 : 2015-09-24 16:30 ~
장소 : 500동 목암홀
Binuclear non-heme iron enzymes composes an expanding class, more of which has been continuously discovered to be involved in essential aerobic metabolism. This class of enzymes catalyzes a wide range of chemistries such as H-atom abstraction, desaturation, hydroxylation, and electrophilic aromatic substitution, utilizing a coupled diiron cofactor that reductively activates O2 as forming several intermediate states that include peroxy-level and high-valent Fe-level intermediates. To understand the diversity in the chemistry of the diiron cofactor, the electronic and geometric structures of these oxygen intermediates need to be defined.
Two different types of peroxy intermediates are known to exist; P and Pˊ display significantly different reactivity and spectroscopic properties. While P could be characterized by resonance Raman rR spectroscopy and shown to have a cis--1,2 peroxy-bridged structure, existing experimental data for Pˊ are too limited for its structural determination. Thus, first, we have characterized the biferrous precursor that forms a relatively stable Pˊ to understand the binding of O¬2 to form Pˊ, using circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field MCD spectroscopic techniques. The study shows a good overlap between the redox-active frontier molecular orbitals of Fe(II) centers and O2 for rapid electron transfer to form a peroxy bridge. Second, we have first obtained vibrational information on Pˊ by employing a synchrotron-based technique called nuclear resonance vibrational spectroscopy (NRVS). Third, these experimentally-established structural differences between P and Pˊ has been further used in DFT studies to clarify their differences in electrophilic reactivity. This understanding of the peroxy-level intermediates is key to elucidating the mechanisms of class Ia ribonucleotide reductase (RR) and soluble methane monooxygenase (MMO), where the peroxy intermediates further convert to reactive high-valent intermediates that abstract an H atom from Tyr in RR and from CH4 in MMO.
Two different types of peroxy intermediates are known to exist; P and Pˊ display significantly different reactivity and spectroscopic properties. While P could be characterized by resonance Raman rR spectroscopy and shown to have a cis--1,2 peroxy-bridged structure, existing experimental data for Pˊ are too limited for its structural determination. Thus, first, we have characterized the biferrous precursor that forms a relatively stable Pˊ to understand the binding of O¬2 to form Pˊ, using circular dichroism (CD), magnetic CD (MCD), and variable-temperature, variable-field MCD spectroscopic techniques. The study shows a good overlap between the redox-active frontier molecular orbitals of Fe(II) centers and O2 for rapid electron transfer to form a peroxy bridge. Second, we have first obtained vibrational information on Pˊ by employing a synchrotron-based technique called nuclear resonance vibrational spectroscopy (NRVS). Third, these experimentally-established structural differences between P and Pˊ has been further used in DFT studies to clarify their differences in electrophilic reactivity. This understanding of the peroxy-level intermediates is key to elucidating the mechanisms of class Ia ribonucleotide reductase (RR) and soluble methane monooxygenase (MMO), where the peroxy intermediates further convert to reactive high-valent intermediates that abstract an H atom from Tyr in RR and from CH4 in MMO.
